Contact with high resistance material insert



June 20, 1967 H. M. PFLANZ CONTACT WITH HIGH RESISTANCE MATERIAL INSERT Filed Nov. 25, 1964 United States Patent 3,327,081 CONTACT WITH HIGH RESISTANCE MATERIAL INSERT Herbert M. Pfianz, Roslindale, Mass., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis. Filed Nov. 25, 1964, Ser. No. 413,794 14 Claims. (Cl. 200144) ABSTRACT OF THE DISCLOSURE A circuit interrupter, such as a vacuum switch, comprises a pair of relatively movable contacts, at least one of which is a relatively flat copper disk having one or more spiral slots extending inwardly from the periphery of the contact to cause rotation of an arc between said cont-acts. The slot is filled with solid material having high electrical resistance, such as nickel or iron, to facilitate movement of the arc terminal across each slot as the arc rotates.

This invention relates generally to means for extinguishing arcs generated between electric terminals or separable contacts. More specifically, it relates to electric terminals or separable contacts wherein an arc established therebetween is rotated to effect its extinguishment.

The are interrupting capacity of a pair of relatively movable circuit breaker contacts, for example, can be increased substantially by rotating the arc terminals at high speed across the surfaces of the contact. Patent 2,949,520, issued Aug. 16, 1960 to H. H. Schneider, for Contact Structure for an Electric Circuit Interrupter, discloses contacts wherein such are terminal rotation is effected by means of one or more slots extending inwardly from the periphery of a disk shaped contact. However, in the type of contact disclosed in the aforesaid Schneider patent, the arc terminal has to jump across the open slots as the arc rotates and there is a tendency for it to hang on at the slot edges before jumping the slot. This results in pitting and burning of the contact surface and results in an increase in the loss of contact material during arcing which is especially undesirable in vacuum switch contacts.

It is an object of the present invention to provide improved electric terminals or contacts of the type which 3,327,081 Patented June 20, 1967 effect preferential arcing on the contact body. Examples of such material combinations are nickel as filler and copper as contact body.

Another object is to provide filler material of the aforesaid character which is made of iron or nickel.

Another object is to provide terminals or contacts of the aforesaid character which are relatively easy to fabricate and are reliable in use.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawing illustrates several preferred embodiments of the invention but it is to be understood that the embodiments illustrated are susceptible of modification with respect to details thereof without departing from the scope of the appended claims.

In the drawing:

FIG. 1 is a cross sectional view of a vacuum interrupter employing one embodiment of a pair of contacts incorporating the present invention;

FIG. 2 is an end view of one of the pair of contacts shown in FIG. 1;

FIG. 3 is a cross sectional view of the contact taken along line III-III of FIG. 2;

FIG. 4 is an end view of another contact embodying the invention; and

FIG. 5 is a cross sectional View of the contact taken along line VV of FIG. 4.

Referring to FIG. 1, the numeral 10 designates a vacuum type electric circuit interrupter or switch employing relatively movable contacts incorporating the present invention. It is to be understood, however, that contacts or electric switches incorporating the present invention can be employed in other types of electrical apparatus beside circuit breakers, such as lightning .arresters for example.

Vacuum switch 10 comprises a cylindrical envelope 12 which may be formed, for example, of a suitable vitreous material. One end of envelope 12 is provided with an annular rim 14 to which is rigidly secured in a vacuum tight connection thereto one end of a ring or flange 16. A metallic cap 18 is sealed along its edge to the other end of flange 16. Cap 18- supports a stationary contact support 20 which extends along the longitudinal axis of envelope 12 and is rigidly supported so as to be restricted supply the arc rotation principle to effect are extinguishagainst longitudinal or laternal movement. The opposite end of envelope 12 is provided with an annular rim 22 to which is rigidly secured in a vacuum tight connection one end of a ring on flange 24. A tube or retainer 2-6 is sealed along its rim in a vacuum tight connection to flange V 24. A metallic cylindrically shaped flexible be1lows28 the slots has high electrical resistance and fills the slots so as to render the contact surface relatively smooth.

Another object is to provide terminals or contacts of the aforesaid character wherein the slots are filled with a material having a high arc voltage as compared tothat of the material of which the contact body is made so as to is rigidly secured in a vacuum tight connection at one end thereof to retainer 26. The other end of bellows 28 surrounds and is rigidly secured in a vacuum tight conneetion to a movable contact support 30 which is arranged to extend through retainer 26 into envelope 12 and is in cooperating relationship with contact support 20.

The relatively movable contact supports 20 and 30 may be made of a suitable electrically conductive material such as copper or the like. Contact support 30 is understood to be arranged for longitudinal movement along its axis for a limited predetermined distance by a suitable contact actuating mechanism (not shown).

The contact supports 20 and 30 support contacts 32 and 34, respectively, hereinafter described. In order to control the dispersion of arcing products emitted upon separation of the contacts 32 an 34, a cylindrical cup shaped tube or shield 36 is provided which is rigidly secured to contact support 20 and is arranged to extend beyond the adjacent ends of both contact supports 20 and 30 so as to surround the contacts 32 and 34 when the contacts are engaged and disengaged. Shield 36 may be formed of glass or any suitable metallic or non-metallic material.

Upon actuation of movable contact support 30 in axial contact engaging or contact disengaging direction, bellows 28 deflects, allowing restricted longitudinal movement of contact 34. The required range of movement of contact 34 is very small. For example, with only A of an inch separation between engaging surfaces of contacts 32 and 34 a current of several thousand amperes at an AC voltage of 18,000 can be safely interrupted. The contacts when engaged can continuously conduct current of several hundred amperes.

Referring to FIG. 1, contacts 32 and 34 are shown as substantially identical to each other and a description of contact 34 will suffice for contact 32 as well. However, it is tobe understood that the invention can be embodied in a circuit interrupter or other arc extinguishing electrical device wherein only one contact or terminal is constructed in accordance with the present invention. FIGS. 1, 2 and 3 show that contact 34 is in the shape of a disk and has its surface facing contact 32. The center of the surface of contact 34 is recessed as shown at 37 and a contact making region 38 surrounds the recess. Thus, when contacts 32 and 34 are closed, the regions 38 abut and current flow through the contacts is in a loop shaped path, as indicated by the broken line 40 in FIG. 3. Upon con-tact separation an arc is initiated between contacts 32 and 34 which has its terminals on contact making region 38. The magnetic effect resulting from the looped path described tends to drive the arc radially outward in accordance with well known principles.

Contact 34 is provided with a single slot 42 which extends radially from the periphery thereof toward the center of the contact. Slot 42 defines a spiral path with respect to the center point of the surface of contact 34 in the embodiment shown the path traverses more than 360 degrees of angular distance. Thus, current flow to an arc terminal at any point near the periphery of contact 34 must flow through the intervening convolutions of the spiral and will generate a force component tangent to the periphery of the contact in the vicinity of the arc to rotate and drive the arc toward the periphery.

In practice, the rapidity of movement of the arc will cause it to jump slot 42 at various places as it rotates. However, there is a tendency for the arc to hang on the surface of contact 34 at the edge of slot 42 before jumping and this results in burning, pitting and a loss of contact material. In accordance with the present invention, the tendency of the arc to hang up is overcome by filling slot 42 of contact 34 with high resistance material 44, such as iron or nickel, so that the material is flush with the surface of the contact. This results in a smooth uninterrupted contact surface across which the arc can travel as it is driven around the contact surface. However, because the material 44 has an electrical resistance characteristic which is higher than that of the material of which the contact is made, the electrical characteristics of a slotted type contact are retained insofar as an arc rotation is concerned.

FIGS. 4 and 5 show another contact 46 embodying the present invention. Contact 46 is provided with a plurality of slots 48 which divide the contact into discrete segments 50. The slots 48 of contact 46 are shown as being generally of spiral configuration but they could have some other configuration and are shown as overlapping one another. An are initiated on one segment 50 in accordance with the principles discussed above is forced outwardly on the segment and is also caused to rotate. As the arc rotates, it is forced to jump from segment 50 to segment 50 across the intervening slot 48 and the tendency for it to hang on at the slot edge is overcome by filling the slots 48 with high resistance material 4 4, such as iron or nickel, so that the material is flush with the surface of contact 46 in accordance with the present invention.

It is known that in vacuum switches the arc voltage depends on the contact material. F or example, contacts of nickel or iron cause a very much higher are voltage than copper. As a result of this the arc has a tendency to root on the lower arc voltage material such as copper when metal combinations are employed in a contact. Thus, in the aforementioned example, if the contact body according to the present invention is made of copper and the slot is filled with iron, there is still the advantage of a smooth contact surface paired with the arc rotating ability. However, the inherent higher interrupting ability of copper as a cont-act material is not lost because of the preferential arcing on the copper. Other metal or alloy combinations may be employed to carry out the present invention provided the materials employed are selected according to the preceding principles.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In electrical apparatus, in combination, a pair of terminals between which an electric arc is established and is to be extinguished, at least one of said terminals comprising an electrically conductive disk having low electrical resistance and having at least one slot extending inwardly from the periphery thereof in a curved path whereby an arc terminal is initiated near the central portion of the surface of the disk and is rotated around said surface toward the periphery thereof, and solid conductive material of high electrical resistance disposed within said slot, said material filling said slot so as to be flush with the surface of said disk.

2. The combination according to claim 1 wherein said slot extends through the entire thickness of said disk.

3. The combination according to claim 1 wherein said material is a high resistance, high are voltage material as compared to the material from which the disk is made.

4. The combination according to claim 1 wherein said material is nickel and the disk is copper.

5. The combination according to claim 1 wherein said material is steel and the disk is copper.

6. The combination according to claim 1 wherein said slot defines a spiral path with respect to the center point of the surface of said disk.

7. The combination according to claim 1 wherein said spiral path extends through an angular distance greater than 360.

8. In electrical apparatus, in combination, a pair of terminals between which an electric arc is established and is to be extinguished, at least one of said terminals comprising an electrically conductive disk having a plurality of slots therein extending inwardly from the periphery thereof whereby an arc terminal initiated near the central portion of the surface of the disk is rotated around said surface and toward the periphery thereof, and solid conductive material of high electrical resistance disposed within said slots, said material filling said slots so as to be flush with the surface of said disk.

9. The combination according to claim 8 wherein said slot extends through the entire thickness of said disk.

10. The combination according to claim 8 wherein said material is a high resistance, high are voltage material as compared to the material from which the disk is made.

11. The combination according to claim -8 wherein said material is steel and the disk is copper.

12. The combination according to claim 8 wherein said material is nickel and the disk is copper.

13. The combination according to claim 8 wherein at least some of said slots extend into angularly overlapping relationship with an adjacentslot.

14. In an electric circuit breaker, in combination, a pair of cooperating contacts relatively movable into and out of engagement with each other, at least one of said contacts comprising an electrically conductive disk of relatively low resistance material having a plurality of slots extending inwardly from its outer periphery whereby an arc initiated near the central portion of the surface of the disk rotates therearound in a peripheral direction, said slots extending through the entire thickness of said disk, at least some of said slots extending into angularly overlapping relation-ship With an adjacent slot, and a high resistance solid conductive material filling said slots and flush with said surface of said disk.

References Cited UNITED STATES PATENTS Hampton et a1. 200-147 X Slepiam 20016 6 Schneider 200144 Polinko et al. 2 00-444 Porter 200-147 Montoya et al. 20016-6 Canada.

ROBERT S. MACON, Primary Examiner. 

1. IN ELECTRICAL APPARATUS, IN COMBINATION, A PAIR OF TERMINALS BETWEEN WHICH AN ELECTRIC ARC IS ESTABLISHED AND IS TO BE EXTINGUISHED AT LEAST ONE OF SAID TERMINALS COMPRISING AN ELECTRICALLY CONDUCTIVE DISK HAVING LOW ELECTRICAL RESISTANCE AND HAVING AT LEAST ONE SLOT EXTENDING INWARDLY FROM THE PERIPHERY THEREOF IN A CURVED PATH WHEREBY AN ARC TERMINAL IS INITIATED NEAR THE CENTRAL PORTION OF THE SURFACE OF THE DISK AND IS ROTATED AROUND SAID SURFACE TOWARD THE PERIPHERY THEREOF, AND SOLID CONDUCTIVE MATERIAL OF HIGH ELECTRICAL RESISTANCE DISPOSED WITHIN SAID SLOT, SAID MATERIAL FILLING SAID SLOT SO AS TO BE FLUSH WITH THE SURFACE OF SAID DISK. 